Re-arrange stored inventory holders

ABSTRACT

Inventory holders in an inventory system can be moved among differing storage positions. The moves can be performed by mobile drive units not otherwise transporting inventory holders directly to or from inventory stations. A free mobile drive unit can move an inventory holder not likely to be useful soon at any nearby station from a storage position near the station to a position farther away from the station. A mobile drive unit can move an inventory holder likely to be useful soon from a storage position farther away from one or more stations to a storage position nearby one or more stations.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/499,047, Filed Sep. 26, 2014, and entitled “RE-ARRANGE STOREDINVENTORY HOLDERS”, the contents of which are herein incorporated byreference in its entirety.

BACKGROUND

Modern inventory systems, such as those in mail order warehouses, supplychain distribution centers, airport luggage systems, and custom-ordermanufacturing facilities, face significant challenges in responding torequests for inventory items. As inventory systems grow, the challengesof simultaneously completing a large number of packing, storing, andother inventory-related tasks become non-trivial. In inventory systemstasked with responding to large numbers of diverse inventory requests,inefficient utilization of system resources, including space, equipment,and manpower, can result in lower throughput, unacceptably long responsetimes, an ever-increasing backlog of unfinished tasks, and, in general,poor system performance. Additionally, expanding or reducing the size orcapabilities of many inventory systems requires significant changes toexisting infrastructure and equipment. As a result, the cost ofincremental changes to capacity or functionality may be prohibitivelyexpensive, limiting the ability of the system to accommodatefluctuations in system throughput.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments in accordance with the present disclosure will bedescribed with reference to the drawings, in which like referencenumerals may represent like parts, and in which:

FIG. 1 illustrates examples of movement of inventory holders amongstorage positions within an inventory system according to a particularembodiment;

FIG. 2 illustrates components of an inventory system according to aparticular embodiment;

FIG. 3 illustrates in greater detail the components of an examplemanagement module that may be utilized in particular embodiments of theinventory system shown in FIG. 2;

FIGS. 4 and 5 illustrate in greater detail an example mobile drive unitthat may be utilized in particular embodiments of the inventory systemshown in FIG. 2;

FIG. 6 illustrates in greater detail an example inventory holder thatmay be utilized in particular embodiments of the inventory system shownin FIG. 2;

FIG. 7 is a flowchart illustrating an example of a process forre-arranging inventory holders based at least in part on predictionsabout the allocation of tasks to stations according to a particularembodiment;

FIG. 8 is a flowchart illustrating an example of a process for movinginventory holders among storage locations based at least in part onutility of such movements according to a particular embodiment;

FIG. 9 is a flowchart illustrating an example of a process for shiftingstorage positions of inventory holders as secondary tasks according to aparticular embodiment; and

FIG. 10 illustrates an environment in which various features of theinventory system can be implemented, in accordance with at least oneembodiment.

DETAILED DESCRIPTION

In the following description, various embodiments will be described. Forpurposes of explanation, specific configurations and details are setforth in order to provide a thorough understanding of the embodiments.However, it will also be apparent to one skilled in the art that theembodiments may be practiced without the specific details. Furthermore,well-known features may be omitted or simplified in order not to obscurethe embodiment being described.

Embodiments herein are directed to an inventory system having multipleinventory holders and drive units for moving the inventory holders.Specifically, features herein are directed to re-arranging inventoryholders within a storage area utilizing mobile drive units that are nototherwise immediately engaged in moving other inventory holders to orfrom a particular station.

In accordance with an embodiment, mobile drive units that mightotherwise sit idle while awaiting another task assignment are taskedwith moving inventory holders into more useful storage positions.Inventory holders may be arranged to facilitate near-future stationactivities such as pick, stow, or count operations.

For example, FIG. 1 depicts an inventory system 10 in which mobile driveunits 20 can be tasked with moving inventory holders 30 among differingstorage positions. The moves can be performed when the mobile driveunits 20 are not otherwise transporting inventory holders 30 directly toor from a station 50, such as when the mobile drive unit 20 is en routeto pick up an inventory holder 30 for a station 50 or when the mobiledrive unit 20 is not occupied with another task. Using such unencumberedmobile drive units 20 to move inventory holders 30 among differingstorage positions may improve efficiency of future tasks involvingtransport of inventory holders 30 between storage and stations 50.

In a first example, a free mobile drive unit 20 may move an inventoryholder 30 that is not used frequently (i.e., an inventory holder with alow utility) at a station 50 from a storage position near the station 50to a position farther away from the station 50 (such as depicted by afirst arrow 12). This action may free up space for storage of aninventory holder 30 that is used more frequently at the station 50(i.e., an inventory holder with a higher utility). In a second example,a mobile drive unit 20 may move an inventory holder 30 with a highutility from a position farther away from the station 50 to a storageposition near the station 50 (such as depicted by a second arrow 14).This action may make the inventory holder 30 more readily available fora future task at the station 50. In a third example, a single mobiledrive unit 20 may move both an inventory holder 30 with a high utilityand an inventory holder 30 with a low utility in order to swap thepositions of the inventory holders 30 relative to the station (such asdepicted by the double-sided arrow 16). This action may help optimizethe arrangement of inventory holders 30 relative to the station 50.

FIG. 2 illustrates the contents of an inventory system 10. Inventorysystem 10 includes a management module 15, one or more mobile driveunits 20, one or more inventory holders 30, and one or more inventorystations 50. Mobile drive units 20 transport inventory holders 30between points within a workspace 70 in response to commandscommunicated by management module 15. Each inventory holder 30 storesone or more types of inventory items. As a result, inventory system 10is capable of moving inventory items between locations within workspace70 to facilitate the entry, processing, and/or removal of inventoryitems from inventory system 10 and the completion of other tasksinvolving inventory items.

Management module 15 assigns tasks to appropriate components ofinventory system 10 and coordinates operation of the various componentsin completing the tasks. These tasks may relate not only to the movementand processing of inventory items, but also to the management andmaintenance of the components of inventory system 10. For example,management module 15 may assign portions of workspace 70 as parkingspaces for mobile drive units 20, the scheduled recharge or replacementof mobile drive unit batteries, the storage of empty inventory holders30, or any other operations associated with the functionality supportedby inventory system 10 and its various components. Management module 15may select components of inventory system 10 to perform these tasks andcommunicate appropriate commands and/or data to the selected componentsto facilitate completion of these operations. Although shown in FIG. 2as a single, discrete component, management module 15 may representmultiple components and may represent or include portions of mobiledrive units 20 or other elements of inventory system 10. As a result,any or all of the interaction between a particular mobile drive unit 20and management module 15 that is described below may, in particularembodiments, represent peer-to-peer communication between that mobiledrive unit 20 and one or more other mobile drive units 20. The contentsand operation of an example embodiment of management module 15 arediscussed further below with respect to FIG. 3.

Mobile drive units 20 move inventory holders 30 between locations withinworkspace 70. Mobile drive units 20 may represent any devices orcomponents appropriate for use in inventory system 10 based on thecharacteristics and configuration of inventory holders 30 and/or otherelements of inventory system 10. In a particular embodiment of inventorysystem 10, mobile drive units 20 represent independent, self-powereddevices configured to freely move about workspace 70. Examples of suchinventory systems are disclosed in U.S. Patent Publication No.2012/0143427, published on Jun. 7, 2012, titled “SYSTEM AND METHOD FORPOSITIONING A MOBILE DRIVE UNIT” and U.S. Pat. No. 8,280,547, issued onOct. 2, 2012, titled “METHOD AND SYSTEM FOR TRANSPORTING INVENTORYITEMS”, the entire disclosures of which are herein incorporated byreference. In alternative embodiments, mobile drive units 20 representelements of a tracked inventory system configured to move inventoryholder 30 along tracks, rails, cables, crane system, or other guidanceor support elements traversing workspace 70. In such an embodiment,mobile drive units 20 may receive power and/or support through aconnection to the guidance elements, such as a powered rail.Additionally, in particular embodiments of inventory system 10 mobiledrive units 20 may be configured to utilize alternative conveyanceequipment to move within workspace 70 and/or between separate portionsof workspace 70. The contents and operation of an example embodiment ofa mobile drive unit 20 are discussed further below with respect to FIGS.4 and 5.

Additionally, mobile drive units 20 may be capable of communicating withmanagement module 15 to receive information identifying selectedinventory holders 30, transmit the locations of mobile drive units 20,or exchange any other suitable information to be used by managementmodule 15 or mobile drive units 20 during operation. Mobile drive units20 may communicate with management module 15 wirelessly, using wiredconnections between mobile drive units 20 and management module 15,and/or in any other appropriate manner. As one example, particularembodiments of mobile drive unit 20 may communicate with managementmodule 15 and/or with one another using 802.11, Bluetooth, or InfraredData Association (IrDA) standards, or any other appropriate wirelesscommunication protocol. As another example, in a tracked inventorysystem 10, tracks or other guidance elements upon which mobile driveunits 20 move may be wired to facilitate communication between mobiledrive units 20 and other components of inventory system 10. Furthermore,as noted above, management module 15 may include components ofindividual mobile drive units 20. Thus, for the purposes of thisdescription and the claims that follow, communication between managementmodule 15 and a particular mobile drive unit 20 may representcommunication between components of a particular mobile drive unit 20.In general, mobile drive units 20 may be powered, propelled, andcontrolled in any manner appropriate based on the configuration andcharacteristics of inventory system 10.

Inventory holders 30 store inventory items. In a particular embodiment,inventory holders 30 include multiple storage bins with each storage bincapable of holding one or more types of inventory items. Inventoryholders 30 are capable of being carried, rolled, and/or otherwise movedby mobile drive units 20. In particular embodiments, inventory holder 30may provide additional propulsion to supplement that provided by mobiledrive unit 20 when moving inventory holder 30.

Additionally, in particular embodiments, inventory items 40 may alsohang from hooks or bars (not shown) within or on inventory holder 30. Ingeneral, inventory holder 30 may store inventory items 40 in anyappropriate manner within inventory holder 30 and/or on the externalsurface of inventory holder 30.

Additionally, each inventory holder 30 may include a plurality of faces,and each bin may be accessible through one or more faces of theinventory holder 30. For example, in a particular embodiment, inventoryholder 30 includes four faces. In such an embodiment, bins located at acorner of two faces may be accessible through either of those two faces,while each of the other bins is accessible through an opening in one ofthe four faces. Mobile drive unit 20 may be configured to rotateinventory holder 30 at appropriate times to present a particular faceand the bins associated with that face to an operator or othercomponents of inventory system 10.

Inventory items represent any objects suitable for storage, retrieval,and/or processing in an automated inventory system 10. For the purposesof this description, “inventory items” may represent any one or moreobjects of a particular type that are stored in inventory system 10.Thus, a particular inventory holder 30 is currently “storing” aparticular inventory item if the inventory holder 30 currently holds oneor more units of that type. As one example, inventory system 10 mayrepresent a mail order warehouse facility, and inventory items mayrepresent merchandise stored in the warehouse facility. Duringoperation, mobile drive units 20 may retrieve inventory holders 30containing one or more inventory items requested in an order to bepacked for delivery to a customer or inventory holders 30 carryingpallets containing aggregated collections of inventory items forshipment. Moreover, in particular embodiments of inventory system 10,boxes containing completed orders may themselves represent inventoryitems.

In particular embodiments, inventory system 10 may also include one ormore inventory stations 50. Inventory stations 50 represent locationsdesignated for the completion of particular tasks involving inventoryitems. Such tasks may include the removal of inventory items frominventory holders 30, the introduction of inventory items into inventoryholders 30, the counting of inventory items in inventory holders 30, thedecomposition of inventory items (e.g. from pallet- or case-sized groupsto individual inventory items), the consolidation of inventory itemsbetween inventory holders 30, and/or the processing or handling ofinventory items in any other suitable manner. In particular embodiments,inventory stations 50 may just represent the physical locations where aparticular task involving inventory items can be completed withinworkspace 70. In alternative embodiments, inventory stations 50 mayrepresent both the physical location and also any appropriate equipmentfor processing or handling inventory items, such as scanners formonitoring the flow of inventory items in and out of inventory system10, communication interfaces for communicating with management module15, and/or any other suitable components. Inventory stations 50 may becontrolled, entirely or in part, by human operators or may be fullyautomated. Moreover, the human or automated operators of inventorystations 50 may be capable of performing certain tasks to inventoryitems, such as packing, counting, or transferring inventory items, aspart of the operation of inventory system 10.

Workspace 70 represents an area associated with inventory system 10 inwhich mobile drive units 20 can move and/or inventory holders 30 can bestored. For example, workspace 70 may represent all or part of the floorof a mail-order warehouse in which inventory system 10 operates. In someembodiments, workspace 70 includes multiple floors, and some combinationof ramps, elevators, conveyors, and/or other devices are provided tofacilitate movement of mobile drive units 20 and/or other components ofthe inventory system 10 between the multiple floors. Although FIG. 2shows, for the purposes of illustration, an embodiment of inventorysystem 10 in which workspace 70 includes a fixed, predetermined, andfinite physical space, particular embodiments of inventory system 10 mayinclude mobile drive units 20 and inventory holders 30 that areconfigured to operate within a workspace 70 that is of variabledimensions and/or an arbitrary geometry. While FIG. 2 illustrates aparticular embodiment of inventory system 10 in which workspace 70 isentirely enclosed in a building, alternative embodiments may utilizeworkspaces 70 in which some or all of the workspace 70 is locatedoutdoors, within a vehicle (such as a cargo ship), or otherwiseunconstrained by any fixed structure.

In operation, management module 15 selects appropriate components tocomplete particular tasks and transmits task assignments 18 to theselected components to trigger completion of the relevant tasks. Eachtask assignment 18 defines one or more tasks to be completed by aparticular component. These tasks may relate to the retrieval, storage,replenishment, and counting of inventory items and/or the management ofmobile drive units 20, inventory holders 30, inventory stations 50 andother components of inventory system 10. Depending on the component andthe task to be completed, a particular task assignment 18 may identifylocations, components, and/or actions associated with the correspondingtask and/or any other appropriate information to be used by the relevantcomponent in completing the assigned task.

In particular embodiments, management module 15 generates taskassignments 18 based, in part, on inventory requests that managementmodule 15 receives from other components of inventory system 10 and/orfrom external components in communication with management module 15.These inventory requests identify particular operations to be completedinvolving inventory items stored or to be stored within inventory system10 and may represent communication of any suitable form. For example, inparticular embodiments, an inventory request may represent a shippingorder specifying particular inventory items that have been purchased bya customer and that are to be retrieved from inventory system 10 forshipment to the customer. Management module 15 may also generate taskassignments 18 independently of such inventory requests, as part of theoverall management and maintenance of inventory system 10. For example,management module 15 may generate task assignments 18 in response to theoccurrence of a particular event (e.g., in response to a mobile driveunit 20 requesting a space to park), according to a predeterminedschedule (e.g., as part of a daily start-up routine), or at anyappropriate time based on the configuration and characteristics ofinventory system 10. After generating one or more task assignments 18,management module 15 transmits the generated task assignments 18 toappropriate components for completion of the corresponding task. Therelevant components then execute their assigned tasks.

With respect to mobile drive units 20 specifically, management module 15may, in particular embodiments, communicate task assignments 18 toselected mobile drive units 20 that identify one or more destinationsfor the selected mobile drive units 20. Management module 15 may selecta mobile drive unit 20 to assign the relevant task based on the locationor state of the selected mobile drive unit 20, an indication that theselected mobile drive unit 20 has completed a previously-assigned task,a predetermined schedule, and/or any other suitable consideration. Thesedestinations may be associated with an inventory request the managementmodule 15 is executing or a management objective the management module15 is attempting to fulfill. For example, the task assignment may definethe location of an inventory holder 30 to be retrieved, an inventorystation 50 to be visited, a storage location where the mobile drive unit20 should park until receiving another task, or a location associatedwith any other task appropriate based on the configuration,characteristics, and/or state of inventory system 10, as a whole, orindividual components of inventory system 10. For example, in particularembodiments, such decisions may be based on the popularity of particularinventory items, the staffing of a particular inventory station 50, thetasks currently assigned to a particular mobile drive unit 20, and/orany other appropriate considerations.

As part of completing these tasks mobile drive units 20 may dock withand transport inventory holders 30 within workspace 70. Mobile driveunits 20 may dock with inventory holders 30 by connecting to, lifting,and/or otherwise interacting with inventory holders 30 in any othersuitable manner so that, when docked, mobile drive units 20 are coupledto and/or support inventory holders 30 and can move inventory holders 30within workspace 70. While the description below focuses on particularembodiments of mobile drive unit 20 and inventory holder 30 that areconfigured to dock in a particular manner, alternative embodiments ofmobile drive unit 20 and inventory holder 30 may be configured to dockin any manner suitable to allow mobile drive unit 20 to move inventoryholder 30 within workspace 70. Additionally, as noted below, inparticular embodiments, mobile drive units 20 represent all or portionsof inventory holders 30. In such embodiments, mobile drive units 20 maynot dock with inventory holders 30 before transporting inventory holders30 and/or mobile drive units 20 may each remain continually docked witha particular inventory holder 30.

While the appropriate components of inventory system 10 completeassigned tasks, management module 15 may interact with the relevantcomponents to ensure the efficient use of space, equipment, manpower,and other resources available to inventory system 10. As one specificexample of such interaction, management module 15 is responsible, inparticular embodiments, for planning the paths mobile drive units 20take when moving within workspace 70 and for allocating use of aparticular portion of workspace 70 to a particular mobile drive unit 20for purposes of completing an assigned task. In such embodiments, mobiledrive units 20 may, in response to being assigned a task, request a pathto a particular destination associated with the task. Moreover, whilethe description below focuses on one or more embodiments in which mobiledrive unit 20 requests paths from management module 15, mobile driveunit 20 may, in alternative embodiments, generate its own paths.

Components of inventory system 10 may provide information to managementmodule 15 regarding their current state, other components of inventorysystem 10 with which they are interacting, and/or other conditionsrelevant to the operation of inventory system 10. This may allowmanagement module 15 to utilize feedback from the relevant components toupdate algorithm parameters, adjust policies, or otherwise modify itsdecision-making to respond to changes in operating conditions or theoccurrence of particular events.

In addition, while management module 15 may be configured to managevarious aspects of the operation of the components of inventory system10, in particular embodiments, the components themselves may also beresponsible for decision-making relating to certain aspects of theiroperation, thereby reducing the processing load on management module 15.

Thus, based on its knowledge of the location, current state, and/orother characteristics of the various components of inventory system 10and an awareness of all the tasks currently being completed, managementmodule 15 can generate tasks, allot usage of system resources, andotherwise direct the completion of tasks by the individual components ina manner that optimizes operation from a system-wide perspective.Moreover, by relying on a combination of both centralized, system-widemanagement and localized, component-specific decision-making, particularembodiments of inventory system 10 may be able to support a number oftechniques for efficiently executing various aspects of the operation ofinventory system 10. As a result, particular embodiments of managementmodule 15 may, by implementing one or more management techniquesdescribed below, enhance the efficiency of inventory system 10 and/orprovide other operational benefits.

FIG. 3 illustrates in greater detail the components of a particularembodiment of management module 15. As shown, the example embodimentincludes a resource scheduling module 92, a route planning module 94, asegment reservation module 96, an inventory module 97, a communicationinterface module 98, a processor 90, and a memory 91. Management module15 may represent a single component, multiple components located at acentral location within inventory system 10, or multiple componentsdistributed throughout inventory system 10. For example, managementmodule 15 may represent components of one or more mobile drive units 20that are capable of communicating information between the mobile driveunits 20 and coordinating the movement of mobile drive units 20 withinworkspace 70. In general, management module 15 may include anyappropriate combination of hardware and/or software suitable to providethe described functionality.

Processor 90 is operable to execute instructions associated with thefunctionality provided by management module 15. Processor 90 maycomprise one or more general purpose computers, dedicatedmicroprocessors, or other processing devices capable of communicatingelectronic information. Examples of processor 90 include one or moreapplication-specific integrated circuits (ASICs), field programmablegate arrays (FPGAs), digital signal processors (DSPs) and any othersuitable specific or general purpose processors.

Memory 91 stores processor instructions, inventory requests, reservationinformation, state information for the various components of inventorysystem 10 and/or any other appropriate values, parameters, orinformation utilized by management module 15 during operation. Memory 91may represent any collection and arrangement of volatile or nonvolatile,local or remote devices suitable for storing data. Examples of memory 91include, but are not limited to, random access memory (RAM) devices,read only memory (ROM) devices, magnetic storage devices, opticalstorage devices, or any other suitable data storage devices.

Resource scheduling module 92 processes received inventory requests andgenerates one or more assigned tasks to be completed by the componentsof inventory system 10. Resource scheduling module 92 may also selectone or more appropriate components for completing the assigned tasksand, using communication interface module 98, communicate the assignedtasks to the relevant components. Additionally, resource schedulingmodule 92 may also be responsible for generating assigned tasksassociated with various management operations, such as prompting mobiledrive units 20 to recharge batteries or have batteries replaced,instructing inactive mobile drive units 20 to park in a location outsidethe anticipated traffic flow or a location near the anticipated site offuture tasks, and/or directing mobile drive units 20 selected for repairor maintenance to move towards a designated maintenance station.

Route planning module 94 receives route requests from mobile drive units20. These route requests identify one or more destinations associatedwith a task the requesting mobile drive unit 20 is executing. Inresponse to receiving a route request, route planning module 94generates a path to one or more destinations identified in the routerequest. Route planning module 94 may implement any appropriatealgorithms utilizing any appropriate parameters, factors, and/orconsiderations to determine the appropriate path. After generating anappropriate path, route planning module 94 transmits a route responseidentifying the generated path to the requesting mobile drive unit 20using communication interface module 98.

Segment reservation module 96 receives reservation requests from mobiledrive units 20 attempting to move along paths generated by routeplanning module 94. These reservation requests request the use of aparticular portion of workspace 70 (referred to herein as a “segment”)to allow the requesting mobile drive unit 20 to avoid collisions withother mobile drive units 20 while moving across the reserved segment. Inresponse to received reservation requests, segment reservation module 96transmits a reservation response granting or denying the reservationrequest to the requesting mobile drive unit 20 using the communicationinterface module 98.

The inventory module 97 maintains information about the location andnumber of inventory items 40 in the inventory system 10. Information canbe maintained about the number of inventory items 40 in a particularinventory holder 30, and the maintained information can include thelocation of those inventory items 40 in the inventory holder 30. Theinventory module 97 can also communicate with the mobile drive units 20,utilizing task assignments 18 to maintain, replenish, or move inventoryitems 40 within the inventory system 10.

Communication interface module 98 facilitates communication betweenmanagement module 15 and other components of inventory system 10,including reservation responses, reservation requests, route requests,route responses, and task assignments. These reservation responses,reservation requests, route requests, route responses, and taskassignments may represent communication of any form appropriate based onthe capabilities of management module 15 and may include any suitableinformation. Depending on the configuration of management module 15,communication interface module 98 may be responsible for facilitatingeither or both of wired and wireless communication between managementmodule 15 and the various components of inventory system 10. Inparticular embodiments, management module 15 may communicate usingcommunication protocols such as 802.11, Bluetooth, or Infrared DataAssociation (IrDA) standards. Furthermore, management module 15 may, inparticular embodiments, represent a portion of mobile drive unit 20 orother components of inventory system 10. In such embodiments,communication interface module 98 may facilitate communication betweenmanagement module 15 and other parts of the same system component.

In general, resource scheduling module 92, route planning module 94,segment reservation module 96, inventory module 97, and communicationinterface module 98 may each represent any appropriate hardware and/orsoftware suitable to provide the described functionality. In addition,as noted above, management module 15 may, in particular embodiments,represent multiple different discrete components and any or all ofresource scheduling module 92, route planning module 94, segmentreservation module 96, inventory module 97, and communication interfacemodule 98 may represent components physically separate from theremaining elements of management module 15. Moreover, any two or more ofresource scheduling module 92, route planning module 94, segmentreservation module 96, inventory module 97, and communication interfacemodule 98 may share common components. For example, in particularembodiments, resource scheduling module 92, route planning module 94,segment reservation module 96, and inventory module 97 representcomputer processes executing on processor 90 and communication interfacemodule 98 comprises a wireless transmitter, a wireless receiver, and arelated computer process executing on processor 90.

FIGS. 4 and 5 illustrate in greater detail the components of aparticular embodiment of mobile drive unit 20. In particular, FIGS. 4and 5 include a front and side view of an example mobile drive unit 20.Mobile drive unit 20 includes a docking head 110, a drive module 120, adocking actuator 130, and a control module 170. Additionally, mobiledrive unit 20 may include one or more sensors configured to detect ordetermine the location of mobile drive unit 20, inventory holder 30,and/or other appropriate elements of inventory system 10. In theillustrated embodiment, mobile drive unit 20 includes a position sensor140, a holder sensor 150, an obstacle sensor 160, and an identificationsignal transmitter 162.

Docking head 110, in particular embodiments of mobile drive unit 20,couples mobile drive unit 20 to inventory holder 30 and/or supportsinventory holder 30 when mobile drive unit 20 is docked to inventoryholder 30. Docking head 110 may additionally allow mobile drive unit 20to maneuver inventory holder 30, such as by lifting inventory holder 30,propelling inventory holder 30, rotating inventory holder 30, and/ormoving inventory holder 30 in any other appropriate manner. Docking head110 may also include any appropriate combination of components, such asribs, spikes, and/or corrugations, to facilitate such manipulation ofinventory holder 30. For example, in particular embodiments, dockinghead 110 may include a high-friction portion that abuts a portion ofinventory holder 30 while mobile drive unit 20 is docked to inventoryholder 30. In such embodiments, frictional forces created between thehigh-friction portion of docking head 110 and a surface of inventoryholder 30 may induce translational and rotational movement in inventoryholder 30 when docking head 110 moves and rotates, respectively. As aresult, mobile drive unit 20 may be able to manipulate inventory holder30 by moving or rotating docking head 110, either independently or as apart of the movement of mobile drive unit 20 as a whole.

Drive module 120 propels mobile drive unit 20 and, when mobile driveunit 20 and inventory holder 30 are docked, inventory holder 30. Drivemodule 120 may represent any appropriate collection of componentsoperable to propel mobile drive unit 20. For example, in the illustratedembodiment, drive module 120 includes motorized axle 122, a pair ofmotorized wheels 124, and a pair of stabilizing wheels 126. Onemotorized wheel 124 is located at each end of motorized axle 122, andone stabilizing wheel 126 is positioned at each end of mobile drive unit20.

Docking actuator 130 moves docking head 110 towards inventory holder 30to facilitate docking of mobile drive unit 20 and inventory holder 30.Docking actuator 130 may also be capable of adjusting the position ororientation of docking head 110 in other suitable manners to facilitatedocking. Docking actuator 130 may include any appropriate components,based on the configuration of mobile drive unit 20 and inventory holder30, for moving docking head 110 or otherwise adjusting the position ororientation of docking head 110. For example, in the illustratedembodiment, docking actuator 130 includes a motorized shaft (not shown)attached to the center of docking head 110. The motorized shaft isoperable to lift docking head 110 as appropriate for docking withinventory holder 30.

Drive module 120 may be configured to propel mobile drive unit 20 in anyappropriate manner. For example, in the illustrated embodiment,motorized wheels 124 are operable to rotate in a first direction topropel mobile drive unit 20 in a forward direction. Motorized wheels 124are also operable to rotate in a second direction to propel mobile driveunit 20 in a backward direction. In the illustrated embodiment, drivemodule 120 is also configured to rotate mobile drive unit 20 by rotatingmotorized wheels 124 in different directions from one another or byrotating motorized wheels 124 at different speeds from one another.

Position sensor 140 represents one or more sensors, detectors, or othercomponents suitable for determining the location of mobile drive unit 20in any appropriate manner. For example, in particular embodiments, theworkspace 70 associated with inventory system 10 includes a number offiducial marks that mark points on a two-dimensional grid that coversall or a portion of workspace 70. In such embodiments, position sensor140 may include a camera and suitable image- and/or video-processingcomponents, such as an appropriately-programmed digital signalprocessor, to allow position sensor 140 to detect fiducial marks withinthe camera's field of view. Control module 170 may store locationinformation that position sensor 140 updates as position sensor 140detects fiducial marks. As a result, position sensor 140 may utilizefiducial marks to maintain an accurate indication of the location mobiledrive unit 20 and to aid in navigation when moving within workspace 70.

Holder sensor 150 represents one or more sensors, detectors, or othercomponents suitable for detecting inventory holder 30 and/ordetermining, in any appropriate manner, the location of inventory holder30, as an absolute location or as a position relative to mobile driveunit 20. Holder sensor 150 may be capable of detecting the location of aparticular portion of inventory holder 30 or inventory holder 30 as awhole. Mobile drive unit 20 may then use the detected information fordocking with or otherwise interacting with inventory holder 30.

Obstacle sensor 160 represents one or more sensors capable of detectingobjects located in one or more different directions in which mobiledrive unit 20 is capable of moving. Obstacle sensor 160 may utilize anyappropriate components and techniques, including optical, radar, sonar,pressure-sensing and/or other types of detection devices appropriate todetect objects located in the direction of travel of mobile drive unit20. In particular embodiments, obstacle sensor 160 may transmitinformation describing objects it detects to control module 170 to beused by control module 170 to identify obstacles and to take appropriateremedial actions to prevent mobile drive unit 20 from colliding withobstacles and/or other objects.

Obstacle sensor 160 may also detect signals transmitted by other mobiledrive units 20 operating in the vicinity of the illustrated mobile driveunit 20. For example, in particular embodiments of inventory system 10,one or more mobile drive units 20 may include an identification signaltransmitter 162 that transmits a drive identification signal. The driveidentification signal indicates to other mobile drive units 20 that theobject transmitting the drive identification signal is in fact a mobiledrive unit. Identification signal transmitter 162 may be capable oftransmitting infrared, ultraviolet, audio, visible light, radio, and/orother suitable signals that indicate to recipients that the transmittingdevice is a mobile drive unit 20.

Additionally, in particular embodiments, obstacle sensor 160 may also becapable of detecting state information transmitted by other mobile driveunits 20. For example, in particular embodiments, identification signaltransmitter 162 may be capable of including state information relatingto mobile drive unit 20 in the transmitted identification signal. Thisstate information may include, but is not limited to, the position,velocity, direction, and the braking capabilities of the transmittingmobile drive unit 20. In particular embodiments, mobile drive unit 20may use the state information transmitted by other mobile drive units toavoid collisions when operating in close proximity with those othermobile drive units.

Control module 170 monitors and/or controls operation of drive module120 and docking actuator 130. Control module 170 may also receiveinformation from sensors such as position sensor 140 and holder sensor150 and adjust the operation of drive module 120, docking actuator 130,and/or other components of mobile drive unit 20 based on thisinformation. Additionally, in particular embodiments, mobile drive unit20 may be configured to communicate with a management device ofinventory system 10 and control module 170 may receive commandstransmitted to mobile drive unit 20 and communicate information back tothe management device utilizing appropriate communication components ofmobile drive unit 20. Control module 170 may include any appropriatehardware and/or software suitable to provide the describedfunctionality. In particular embodiments, control module 170 includes ageneral-purpose microprocessor programmed to provide the describedfunctionality. Additionally, control module 170 may include all orportions of docking actuator 130, drive module 120, position sensor 140,and/or holder sensor 150, and/or share components with any of theseelements of mobile drive unit 20.

Moreover, in particular embodiments, control module 170 may includehardware and software located in components that are physically distinctfrom the device that houses drive module 120, docking actuator 130,and/or the other components of mobile drive unit 20 described above. Forexample, in particular embodiments, each mobile drive unit 20 operatingin inventory system 10 may be associated with a software process(referred to here as a “drive agent”) operating on a server that is incommunication with the device that houses drive module 120, dockingactuator 130, and other appropriate components of mobile drive unit 20.This drive agent may be responsible for requesting and receiving tasks,requesting and receiving routes, transmitting state informationassociated with mobile drive unit 20, and/or otherwise interacting withmanagement module 15 and other components of inventory system 10 onbehalf of the device that physically houses drive module 120, dockingactuator 130, and the other appropriate components of mobile drive unit20. As a result, for the purposes of this description and the claimsthat follow, the term “mobile drive unit” includes software and/orhardware, such as agent processes, that provides the describedfunctionality on behalf of mobile drive unit 20 but that may be locatedin physically distinct devices from the drive module 120, dockingactuator 130, and/or the other components of mobile drive unit 20described above.

While FIGS. 4 and 5 illustrate a particular embodiment of mobile driveunit 20 containing certain components and configured to operate in aparticular manner, mobile drive unit 20 may represent any appropriatecomponent and/or collection of components configured to transport and/orfacilitate the transport of inventory holders 30. As another example,mobile drive unit 20 may represent part of an overhead crane system inwhich one or more crane assemblies are capable of moving within anetwork of wires or rails to a position suitable to dock with aparticular inventory holder 30. After docking with inventory holder 30,the crane assembly may then lift inventory holder 30 and move inventoryto another location for purposes of completing an assigned task.

Furthermore, in particular embodiments, mobile drive unit 20 mayrepresent all or a portion of inventory holder 30. Inventory holder 30may include motorized wheels or any other components suitable to allowinventory holder 30 to propel itself. As one specific example, a portionof inventory holder 30 may be responsive to magnetic fields. Inventorysystem 10 may be able to generate one or more controlled magnetic fieldscapable of propelling, maneuvering, and/or otherwise controlling theposition of inventory holder 30 as a result of the responsive portion ofinventory holder 30. In such embodiments, mobile drive unit 20 mayrepresent the responsive portion of inventory holder 30 and/or thecomponents of inventory system 10 responsible for generating andcontrolling these magnetic fields. While this description providesseveral specific examples, mobile drive unit 20 may, in general,represent any appropriate component and/or collection of componentsconfigured to transport and/or facilitate the transport of inventoryholders 30.

FIG. 6 illustrates in greater detail the components of a particularembodiment of inventory holder 30. In particular, FIG. 6 illustrates thestructure and contents of one side of an example inventory holder 30. Ina particular embodiment, inventory holder 30 may comprise any number offaces with similar or different structure. As illustrated, inventoryholder 30 includes a frame 310, a plurality of legs 328, and dockingsurface 350.

Frame 310 holds inventory items 40. Frame 310 provides storage space forstoring inventory items 40 external or internal to frame 310. Thestorage space provided by frame 310 may be divided into a plurality ofinventory bins 320, each capable of holding inventory items 40.Inventory bins 320 may include any appropriate storage elements, such asbins, compartments, or hooks.

In a particular embodiment, frame 310 is composed of a plurality oftrays 322 stacked upon one another and attached to or stacked on a base318. In such an embodiment, inventory bins 320 may be formed by aplurality of adjustable dividers 324 that may be moved to resize one ormore inventory bins 320. In alternative embodiments, frame 310 mayrepresent a single inventory bin 320 that includes a single tray 322 andno adjustable dividers 324. In some embodiments, a frame 310 and/or aninventory bin 320 of an inventory holder 30 may be designed toaccommodate one or more pallets for inventory items 40. Additionally, inparticular embodiments, frame 310 may represent a load-bearing surfacemounted on mobility element 330. Inventory items 40 may be stored onsuch an inventory holder 30 by being placed on frame 310. In general,frame 310 may include storage internal and/or external storage spacedivided into any appropriate number of inventory bins 320 in anyappropriate manner.

Additionally, in a particular embodiment, frame 310 may include aplurality of device openings 326 that allow mobile drive unit 20 toposition docking head 110 adjacent docking surface 350. The size, shape,and placement of device openings 326 may be determined based on thesize, the shape, and other characteristics of the particular embodimentof mobile drive unit 20 and/or inventory holder 30 utilized by inventorysystem 10. For example, in the illustrated embodiment, frame 310includes four legs 328 that form device openings 326 and allow mobiledrive unit 20 to position mobile drive unit 20 under frame 310 andadjacent to docking surface 350. The length of legs 328 may bedetermined based on a height of mobile drive unit 20.

Docking surface 350 comprises a portion of inventory holder 30 thatcouples to, abuts, and/or rests upon a portion of docking head 110, whenmobile drive unit 20 is docked to inventory holder 30. Additionally,docking surface 350 supports a portion or all of the weight of inventoryholder 30 while inventory holder 30 is docked with mobile drive unit 20.The composition, shape, and/or texture of docking surface 350 may bedesigned to facilitate maneuvering of inventory holder 30 by mobiledrive unit 20. For example, as noted above, in particular embodiments,docking surface 350 may comprise a high-friction portion. When mobiledrive unit 20 and inventory holder 30 are docked, frictional forcesinduced between docking head 110 and this high-friction portion mayallow mobile drive unit 20 to maneuver inventory holder 30.Additionally, in particular embodiments, docking surface 350 may includeappropriate components suitable to receive a portion of docking head110, couple inventory holder 30 to mobile drive unit 20, and/orfacilitate control of inventory holder 30 by mobile drive unit 20.

Holder identifier 360 marks a predetermined portion of inventory holder30 and mobile drive unit 20 may use holder identifier 360 to align withinventory holder 30 during docking and/or to determine the location ofinventory holder 30. More specifically, in particular embodiments,mobile drive unit 20 may be equipped with components, such as holdersensor 150, that can detect holder identifier 360 and determine itslocation relative to mobile drive unit 20. As a result, mobile driveunit 20 may be able to determine the location of inventory holder 30 asa whole. For example, in particular embodiments, holder identifier 360may represent a reflective marker that is positioned at a predeterminedlocation on inventory holder 30 and that holder sensor 150 can opticallydetect using an appropriately-configured camera.

Depending on the configuration and characteristics of mobile drive unit20 and inventory system 10, mobile drive unit 20 may move inventoryholder 30 using a variety of appropriate methods. In a particularembodiment, mobile drive unit 20 is capable of moving inventory holder30 along a two-dimensional grid, combining movement along straight-linesegments with ninety-degree rotations and arcing paths to transportinventory holder 30 from the first location to the second location.Additionally, while moving, mobile drive unit 20 may use fixed objectslocated in the workspace as reference points to assist in navigation.For example, in particular embodiments, inventory system 10 includesmultiple fiducial marks. Mobile drive unit 20 may be configured todetect fiducial marks and to determine the location of mobile drive unit20 and/or measure its movement based on the detection of fiducial marks.

After mobile drive unit 20 arrives at the second location, mobile driveunit 20 may perform appropriate operations to facilitate access toinventory items 40 stored in inventory holder 30. For example, mobiledrive unit 20 may rotate inventory holder 30 to present a particularface of inventory holder 30 to an operator of inventory system 10 orother suitable party, such as a packer selecting inventory items 40 frominventory holder 30. Mobile drive unit 20 may also undock from inventoryholder 30. Alternatively, instead of undocking at the second location,mobile drive unit 20 may transport inventory holder 30 back to the firstlocation or to a third location after any appropriate actions have beentaken involving inventory items 40. For example, after a packer hasremoved particular inventory items 40 from inventory holder 30, mobiledrive unit 20 may return inventory holder 30 to its original storagelocation, a new storage location, or another inventory station. Mobiledrive unit 20 may then undock from inventory holder 30 at this newlocation.

As described above, embodiments herein are directed to re-arranginginventory holders 30 within a storage area utilizing mobile drive units20 that are not otherwise immediately engaged in moving other inventoryholders 30 to or from a particular station 50. The storage area mayinclude storage locations or spaces for storing inventory holders 30when the inventory holders 30 are not at a station 50, not en route to astation 50, not en route from a station 50, or otherwise not affiliatedwith a station 50.

In some embodiments, inventory holders 30 may be re-arranged based atleast in part on predictions about the allocation of tasks to stations50. FIG. 7 is a flowchart illustrating an example of a process 500 forsuch a prediction-based re-arranging of inventory holders 30. At 510,the management module 15 can access (e.g., retrieve, receive, and/orgenerate, as non-limiting examples) a set of designated tasks. This setcan include tasks that are designated for performance in associationwith a particular station 50.

At 520, the management module 15 can instruct movement of inventoryholders 30 for the designated tasks. For example, the management module15 can instruct mobile drive units 20 to move inventory holders 30 thatsatisfy criteria of tasks designated for a station 50. The managementmodule 15 can instruct mobile drive units 20 to move inventory holders30 to, at, or from stations 50 designated for tasks involving theinventory holders 30.

At 530, management module 15 can determine a set of predicted tasks.This set can include tasks that are predicted to be—but not yetdesignated to be—performed in association with a particular station 50,i.e., predicted movements of inventory holders 30 to, at, and/or from aparticular station 50. For example, the management module 15 mayallocate tasks to components within the inventory system 10 that aredetermined to have sufficient capacity to receive task assignments 18and, based on the parameters of the allocated tasks, predict whichcomponents are likely to soonest have capacity anew and thus receivesubsequent task assignments 18 to move inventory holders 30 to, at,and/or from particular stations 50.

At 540, the management module 15 can instruct movement of inventoryholders 30 to facilitate the predicted tasks. For example, themanagement module 15 can instruct mobile drive units 20 to moveinventory holders 30 closer to stations 50 predicted to soon utilizethose inventory holders 30 and/or further from stations 50 predicted notto use those inventory holders 30 within an anticipated timeframe.

As an illustrative example, the process 500 is utilized with respect toa station 50 configured for stowing operations, e.g., operations inwhich inventory items 40 are introduced into the inventory system 10 byloading into open inventory bins 320 of inventory holders 30. Forexample, inventory items 40 may be transferred to pallets, containers,trays, or any other suitable receptacle of an inventory holder 30 at thestow station 50. At 510, the management module 15 can determine a set ofdesignated tasks that involve identifying and moving, for example, thethree closest inventory holders 30 having open inventory bins 320 tothree available station locations (e.g., spaces at the station 50configured to receive inventory holders 30 for performance of relatedtasks). At 520, the management module can identify and instruct threenearby available mobile drive units 20 to move the identified threeclosest open inventory holders 30. At 530, in determining a set ofpredicted tasks for the stow station 50, the management module 15determines that future tasks associated with the stow station 50 willinvolve obtaining additional open inventory holders 30 from variouspositions within the inventory system 10. At 540, the management module15 instructs additional mobile drive units 20 to move additional openinventory holders 30 to storage positions closer to the stow station 50to facilitate the predicted future tasks of obtaining open inventoryholders 30 near the stow station 50.

As another illustrative example, the process 500 is utilized withrespect to a station 50 configured for counting operations, e.g.,operations in which an operator counts to verify or determine a numberof inventory items 40 in a questioned inventory bin 320. For example,inventory items 40 may be counted relative to any particular pallet,container, tray, or any other suitable receptacle of an inventory holder30 at the count station 50. At 510, the management module 15 candetermine a set of designated tasks that involve identifying and moving,for example, the three closest inventory holders 30 having questionedinventory bins 320 to three available spaces at the count station 50. At520, the management module can identify and instruct three nearbyavailable mobile drive units 20 to move the identified three closestquestioned inventory holders 30. At 530, in determining a set ofpredicted tasks for the count station 50, the management module 15determines that future tasks associated with the count station 50 willinvolve obtaining additional questioned inventory holders 30 fromvarious positions within the inventory system 10. At 540, the managementmodule 15 instructs additional mobile drive units 20 to move additionalquestioned inventory holders 30 to storage positions closer to the countstation 50 to facilitate the predicted future tasks of obtainingquestioned inventory holders 30 near the count station 50.

As a further illustrative example, the process 500 is utilized withrespect to a station 50 configured for picking operations, e.g.,operations in which ordered inventory items 40 are obtained from theinventory system 10 by removal from inventory holders 30 containing theordered inventory item 40. For example, inventory items 40 may betransferred from pallets, containers, trays, or any other suitablereceptacle of an inventory holder 30 at the pick station 50. At 510, themanagement module 15 can determine a set of designated tasks thatinvolve identifying and moving, for example, the three closest inventoryholders 30 having ordered inventory items 40 to three available spacesat the pick station 50. At 520, the management module can identify andinstruct three nearby available mobile drive units 20 to move the threeidentified inventory holders 30 to the pick station 50. At 530, indetermining a set of predicted tasks for the pick station 50, themanagement module 15 determines that future tasks associated with thepick station 50 will involve obtaining inventory holders 30 withparticular inventory items 40 from various positions within theinventory system 10 for orders predicted for the pick station 50. At540, the management module 15 instructs additional mobile drive units 20to move inventory holders 30 with the particular inventory items 40 forthe predicted orders to storage positions closer to the pick station 50to facilitate the predicted future tasks of obtaining such inventoryholders 30 near the pick station 50.

In some embodiments, inventory holders 30 may be moved among storagepositions based at least in part on a utility of such movements. FIG. 8is a flowchart illustrating an example of a process 600 for such autility-based movement of inventory holders 30.

At 610, the management module can determine possible movements ofinventory holders 30 among storage locations. For example, for aparticular inventory holder 30, the management module 15 may determinealternate storage spaces that are available and mobile drive units 20that are available to move the inventory holder 30 to each alternatestorage space. In some embodiments, the management module 15 evaluatespossible movements for all inventory holders 30 of the inventory system10. In other embodiments, the management module 15 evaluates possiblemovements for a subset of all inventory holders 30. For example, themanagement module 15 may evaluate possible movements for a subset ofinventory holders 30 that meet criteria associated with tasks associatedwith a particular station 50, such as movements that will move the mostuseful inventory holders 30 closer to the particular station. As anotherexample, the management module 15 may evaluate possible movements for asubset of inventory holders 30 that fail criteria associated with tasksassociated with a particular station 50, such as movements that willtake these less useful inventory holders 30 farther away from theparticular station 50. Such movements may increase an amount of storagespace near the station 50 for inventory holders 30 that are more usefulto that station 50.

At 620, the management module 15 can determine a utility of the possiblemovements. The utility represents the usefulness of a set of movementsoffset by the cost of those movements. For example, the managementmodule 15 may assign a utility score to each of the set of possiblemovements. The utility score can incorporate a number of factors, suchas a drive time involved in a particular movement for a mobile driveunit 20, an amount (e.g., of time or distance) a mobile drive unit 20would deviate from other tasks to perform the particular movement, achange in distance of an inventory holder 30 relative to a particularstation 50 provided by a particular movement, a degree to which contentsof the inventory holder 30 match criteria or demands of a particularstation 50, a timeframe of the demands of a particular station 50,and/or scores representing future gains and/or losses in total systemefficiency. As illustrative examples, utility scores may be higher formovements that involve a shorter drive time for an available mobiledrive unit 20, a smaller amount of deviation from other tasks for amobile drive unit 20, a decrease in distance to a station 50 of aninventory holder 30 likely to soon be useful at that station 50, anincrease in distance to a station 50 of an inventory holder 30 unlikelyto soon be useful at that station 50, an inventory holder 30 with manycontents that match criteria or demands of a particular station 50,facilitating high urgency demands of a particular station 50,anticipated increased gains in total system efficiency, and/oranticipated reduced losses in total system efficiency.

At 630, the management module 15 can instruct the performance ofpossible movement based on the utility of the movements. For example,the management module 15 may compare utility scores to a threshold andinstruct mobile drive units 20 to perform the movements having scoresexceeding the threshold. In another example, the management module 15may compare utility scores of various movements and instruct mobiledrive units 20 to perform the movements with the highest relativeutility scores.

As a simplified illustrative example of the process 600, at 610, themanagement module determines that possible movements include using anavailable mobile drive unit 20 for moving a first inventory holder 30 ora second inventory holder 30 to an open storage location. At 620, themanagement module 15 determines a utility score of 0.75 for moving thefirst inventory holder 30 (e.g., based on a drive time of 20 seconds andthe inventory holder 30 including three out of five items anticipated tobe needed at a station 10 seconds from the open storage location) and autility score of 0.80 for moving the second inventory holder 30 (e.g.,based on a drive time of 25 seconds and the inventory holder 30including four out of five items anticipated to be needed at anotherstation 5 seconds from the open storage location). At 630, themanagement module 15 determines that both movements are greater than aset minimum utility score threshold of 0.50, and instructs the movementof the second inventory holder 30, based on the utility score of 0.8 forthat movement being greater than the 0.75 utility score associated withmoving the first inventory holder 30.

In some embodiments, shifting storage positions of inventory holders 30may be secondary to other tasks. FIG. 9 is a flowchart illustrating anexample of a process 700 for shifting storage positions of inventoryholders 30 as secondary tasks.

At 710, the management module 15 can provide primary instructions tomove inventory holders 30 to, at, and/or from stations 50. For example,the management module 15 may provide instructions to a first set ofmobile drive units 20 to carry out these primary tasks.

At 720, the management module 15 can provide secondary instructions tomove inventory holders 30 among storage locations. For example, themanagement module 15 may provide instructions to a second set of mobiledrive units 20 to carry out these secondary tasks of altering thestorage locations of inventory holders 30. In some embodiments, themanagement module 15 assigns the storage-shifting tasks to mobile driveunits 20 that are not occupied with primary tasks of moving inventoryholders 30 for stations 50. Alternatively or additionally, the secondarystorage-shifting tasks can be assigned to the first set of mobile driveunits 20 en route to pick up—but not yet carrying—inventory holders 30for primary tasks. The secondary tasks may facilitate the primary tasks,such as by bringing inventory holders 30 closer to a station 50 forpick-up during a primary task or clearing space nearer the station 50 toreduce an amount of time to a drop-off location when transporting aninventory holder 30 away from a station 50 during a primary task.

The management module 15 may operate a first set of mobile drive units20 for primary tasks and a second set of mobile drive units 20 forsecondary tasks. In some embodiments, the first set and the second setare distinct sets without overlap. Such an arrangement may ensure thatat least some mobile drive units 20 are always available for secondarytasks. In other embodiments, mobile drive units 20 may operate in eitherof the first set and the second set, such that all mobile drive units 20can perform either primary or secondary tasks. For example, the secondset may include whatever mobile drive units 20 are not occupied withprimary tasks in a particular time interval. The mobile drive units 20in the second set may be configured to receive primary tasks as theprimary tasks come available and/or abort or abandon secondary taskswhen inconsistent with received primary tasks. Such an arrangement mayensure that all mobile drive units 20 are always available for primarytasks. In some embodiments, all mobile drive units 20 may be assignedsecondary tasks at once. For example, before an operator shift starts(e.g., when there may be no primary tasks due to the stations 50 not yetbeing operational), all mobile drive units 20 may be assigned torearranging inventory holders 30 to facilitate operations expected to beperformed at particular stations 50 upon commencement of the shift.

Any number of mobile drive units 20 may be utilized to shift the storagepositions of any number of inventory holders 30. For example, asdescribed above with respect to FIG. 1, a two-way swap of the storagepositions of a high utility inventory holder 30 and a low utilityinventory holder 30 may be performed by a single mobile drive unit 20respectively moving both inventory holders 30 (such as depicted by arrow16). However, a second mobile drive unit 20 could alternatively move oneof the inventory holders 30 while the first mobile drive unit 20 movedthe other inventory holder 30 to effect the same two-way swap. In someembodiments, more than two inventory holders 30 can be involved in asingle swap. For example, three mobile drive units 20 could each move arespective inventory holder 30 from a respective near, intermediate, andfar storage position, relative to a station 50, in a three-way swap inorder to re-locate each respective inventory holder 30 into one of thestorage spaces vacated by the other inventory holders 30. As may beappreciated, two-way, three-way, and up to n-way swaps (in which “n”corresponds to any number) may be performed.

FIG. 10 illustrates aspects of an example environment 1000 forimplementing aspects in accordance with various embodiments. As will beappreciated, although a Web-based environment is used for purposes ofexplanation, different environments may be used, as appropriate, toimplement various embodiments. The environment includes an electronicclient device 1002, which can include any appropriate device operable tosend and receive requests, messages, or information over an appropriatenetwork 1004 and convey information back to a user of the device.Examples of such client devices include personal computers, cell phones,handheld messaging devices, laptop computers, set-top boxes, personaldata assistants, electronic book readers, and the like. The network caninclude any appropriate network, including an intranet, the Internet, acellular network, a local area network or any other such network orcombination thereof. Components used for such a system can depend atleast in part upon the type of network and/or environment selected.Protocols and components for communicating via such a network are wellknown and will not be discussed herein in detail. Communication over thenetwork can be enabled by wired or wireless connections and combinationsthereof. In this example, the network includes the Internet, as theenvironment includes a Web server 1006 for receiving requests andserving content in response thereto, although for other networks analternative device serving a similar purpose could be used as would beapparent to one of ordinary skill in the art.

The illustrative environment includes at least one application server1008 and a data store 1010. It should be understood that there can beseveral application servers, layers, or other elements, processes orcomponents, which may be chained or otherwise configured, which caninteract to perform tasks such as obtaining data from an appropriatedata store. As used herein the term “data store” refers to any device orcombination of devices capable of storing, accessing, and retrievingdata, which may include any combination and number of data servers,databases, data storage devices and data storage media, in any standard,distributed or clustered environment. The application server can includeany appropriate hardware and software for integrating with the datastore as needed to execute aspects of one or more applications for theclient device, handling a majority of the data access and business logicfor an application. The application server provides access controlservices in cooperation with the data store and is able to generatecontent such as text, graphics, audio and/or video to be transferred tothe user, which may be served to the user by the Web server in the formof HyperText Markup Language (“HTML”), Extensible Markup Language(“XML”) or another appropriate structured language in this example. Thehandling of all requests and responses, as well as the delivery ofcontent between the client device 1002 and the application server 1008,can be handled by the Web server. It should be understood that the Weband application servers are not required and are merely examplecomponents, as structured code discussed herein can be executed on anyappropriate device or host machine as discussed elsewhere herein.

The data store 1010 can include several separate data tables, databasesor other data storage mechanisms and media for storing data relating toa particular aspect. For example, the data store illustrated includesmechanisms for storing information which can be used by modulesdescribed herein, such as resource scheduling information 1012, routeplanning information 1014, segment reservation information 1016, and/orinventory information 1018. It should be understood that there can bemany other aspects that may need to be stored in the data store, such asfor page image information and to access right information, which can bestored in any of the above listed mechanisms as appropriate or inadditional mechanisms in the data store 1010. The data store 1010 isoperable, through logic associated therewith, to receive instructionsfrom the application server 1008 and obtain, update or otherwise processdata in response thereto.

Each server typically will include an operating system that providesexecutable program instructions for the general administration andoperation of that server and typically will include a computer-readablestorage medium (e.g., a hard disk, random access memory, read onlymemory, etc.) storing instructions that, when executed by a processor ofthe server, allow the server to perform its intended functions. Suitableimplementations for the operating system and general functionality ofthe servers are known or commercially available and are readilyimplemented by persons having ordinary skill in the art, particularly inlight of the disclosure herein.

The environment in one embodiment is a distributed computing environmentutilizing several computer systems and components that areinterconnected via communication links, using one or more computernetworks or direct connections. However, it will be appreciated by thoseof ordinary skill in the art that such a system could operate equallywell in a system having fewer or a greater number of components than areillustrated in FIG. 10. Thus, the depiction of the system 1000 in FIG.10 should be taken as being illustrative in nature and not limiting tothe scope of the disclosure.

The various embodiments further can be implemented in a wide variety ofoperating environments, which in some cases can include one or more usercomputers, computing devices or processing devices which can be used tooperate any of a number of applications. User or client devices caninclude any of a number of general purpose personal computers, such asdesktop or laptop computers running a standard operating system, as wellas cellular, wireless and handheld devices running mobile software andcapable of supporting a number of networking and messaging protocols.Such a system also can include a number of workstations running any of avariety of commercially-available operating systems and other knownapplications for purposes such as development and database management.These devices also can include other electronic devices, such as dummyterminals, thin-clients, gaming systems and other devices capable ofcommunicating via a network.

Most embodiments utilize at least one network that would be familiar tothose skilled in the art for supporting communications using any of avariety of commercially-available protocols, such as TransmissionControl Protocol/Internet Protocol (“TCP/IP”), Open SystemInterconnection (“OSI”), File Transfer Protocol (“FTP”), Universal Plugand Play (“UpnP”), Network File System (“NFS”), Common Internet FileSystem (“CIFS”) and AppleTalk. The network can be, for example, a localarea network, a wide-area network, a virtual private network, theInternet, an intranet, an extranet, a public switched telephone network,an infrared network, a wireless network, and/or any combination thereof.

In embodiments utilizing a Web server, the Web server can run any of avariety of server or mid-tier applications, including Hypertext TransferProtocol (“HTTP”) servers, FTP servers, Common Gateway Interface (“CGI”)servers, data servers, Java servers and business application servers.The server(s) also may be capable of executing programs or scripts inresponse requests from user devices, such as by executing one or moreWeb applications that may be implemented as one or more scripts orprograms written in any programming language, such as Java®, C, C# orC++, or any scripting language, such as Perl, Python or TCL, as well ascombinations thereof. The server(s) may also include database servers,including without limitation those commercially available from Oracle®,Microsoft®, Sybase® and IBM®.

The environment can include a variety of data stores and other memoryand storage media as discussed above. These can reside in a variety oflocations, such as on a storage medium local to (and/or resident in) oneor more of the computers or remote from any or all of the computersacross the network. In a particular set of embodiments, the informationmay reside in a storage-area network (“SAN”) familiar to those skilledin the art. Similarly, any necessary files for performing the functionsattributed to the computers, servers or other network devices may bestored locally and/or remotely, as appropriate. Where a system includescomputerized devices, each such device can include hardware elementsthat may be electrically coupled via a bus, the elements including, forexample, at least one central processing unit (“CPU”), at least oneinput device (e.g., a mouse, keyboard, controller, touch screen orkeypad) and at least one output device (e.g., a display device, printeror speaker). Such a system may also include one or more storage devices,such as disk drives, optical storage devices and solid-state storagedevices such as random access memory (“RAM”) or read-only memory(“ROM”), as well as removable media devices, memory cards, flash cards,etc.

Such devices also can include a computer-readable storage media reader,a communications device (e.g., a modem, a network card (wireless orwired), an infrared communication device, etc.) and working memory asdescribed above. The computer-readable storage media reader can beconnected with, or configured to receive, a computer-readable storagemedium, representing remote, local, fixed, and/or removable storagedevices as well as storage media for temporarily and/or more permanentlycontaining, storing, transmitting, and retrieving computer-readableinformation. The system and various devices also typically will includea number of software applications, modules, services or other elementslocated within at least one working memory device, including anoperating system and application programs, such as a client applicationor Web browser. It should be appreciated that alternate embodiments mayhave numerous variations from that described above. For example,customized hardware might also be used and/or particular elements mightbe implemented in hardware, software (including portable software, suchas applets) or both. Further, connection to other computing devices suchas network input/output devices may be employed.

Storage media and computer readable media for containing code, orportions of code, can include any appropriate media known or used in theart, including storage media and communication media, such as but notlimited to volatile and non-volatile, removable and non-removable mediaimplemented in any method or technology for storage and/or transmissionof information such as computer readable instructions, data structures,program modules or other data, including RAM, ROM, Electrically ErasableProgrammable Read-Only Memory (“EEPROM”), flash memory or other memorytechnology, Compact Disc Read-Only Memory (“CD-ROM”), digital versatiledisk (DVD) or other optical storage, magnetic cassettes, magnetic tape,magnetic disk storage or other magnetic storage devices or any othermedium which can be used to store the desired information and which canbe accessed by the a system device. Based at least in part on thedisclosure and teachings provided herein, a person of ordinary skill inthe art will appreciate other ways and/or methods to implement thevarious embodiments.

The specification and drawings are, accordingly, to be regarded in anillustrative rather than a restrictive sense. It will, however, beevident that various modifications and changes may be made thereuntowithout departing from the broader spirit and scope of the disclosure asset forth in the claims.

Other variations are within the spirit of the present disclosure. Thus,while the disclosed techniques are susceptible to various modificationsand alternative constructions, certain illustrated embodiments thereofare shown in the drawings and have been described above in detail. Itshould be understood, however, that there is no intention to limit theinvention to the specific form or forms disclosed, but on the contrary,the intention is to cover all modifications, alternative constructionsand equivalents falling within the spirit and scope of the invention, asdefined in the appended claims.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the disclosed embodiments (especially in thecontext of the following claims) are to be construed to cover both thesingular and the plural, unless otherwise indicated herein or clearlycontradicted by context. The terms “comprising,” “having,” “including,”and “containing” are to be construed as open-ended terms (i.e., meaning“including, but not limited to,”) unless otherwise noted. The term“connected” is to be construed as partly or wholly contained within,attached to, or joined together, even if there is something intervening.Recitation of ranges of values herein are merely intended to serve as ashorthand method of referring individually to each separate valuefalling within the range, unless otherwise indicated herein and eachseparate value is incorporated into the specification as if it wereindividually recited herein. All methods described herein can beperformed in any suitable order unless otherwise indicated herein orotherwise clearly contradicted by context. The use of any and allexamples, or exemplary language (e.g., “such as”) provided herein, isintended merely to better illuminate embodiments of the invention anddoes not pose a limitation on the scope of the invention unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe invention.

Preferred embodiments of this disclosure are described herein, includingthe best mode known to the inventors for carrying out the invention.Variations of those preferred embodiments may become apparent to thoseof ordinary skill in the art upon reading the foregoing description. Theinventors expect skilled artisans to employ such variations asappropriate and the inventors intend for the invention to be practicedotherwise than as specifically described herein. Accordingly, thisinvention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw. Moreover, any combination of the above-described elements in allpossible variations thereof is encompassed by the invention unlessotherwise indicated herein or otherwise clearly contradicted by context.

All references, including publications, patent applications, andpatents, cited herein are hereby incorporated by reference to the sameextent as if each reference were individually and specifically indicatedto be incorporated by reference and were set forth in its entiretyherein.

What is claimed is:
 1. An inventory system, comprising: mobile driveunits configured to move inventory holders that are configured to storeinventory items; and a management module configured to: access adesignated set of tasks comprising tasks designated for performance at astation that is configured for performance of a task related to one ormore inventory items associated with an inventory holder when theinventory holder is positioned at the station; instruct a first set ofthe mobile drive units to move respective inventory holders of a firstset of inventory holders from respective storage locations to thestation, the respective inventory holders of the first set of inventoryholders meeting criteria of respective tasks of the designated set oftasks, each storage location for storing an inventory holder apart fromthe station when the inventory holder is not at the station, not beingtransported en route to the station, and not being transported en routefrom the station; determine a predicted set of tasks comprising taskspredicted to be designated for performance at the station; and instructa second set of the mobile drive units to move respective inventoryholders of a second set of inventory holders from respective initialstorage locations to respective subsequent storage locations closer tothe station, the respective inventory holders of the second set ofinventory holders meeting criteria of respective tasks of the predictedset of tasks.
 2. The inventory system of claim 1, wherein the managementmodule is further configured to instruct a third set of the mobile driveunits to move respective inventory holders of a third set of inventoryholders from respective initial storage locations to respectivesubsequent storage locations further from the station, the inventoryholders of the third set of inventory holders not meeting criteria ofrespective tasks of the predicted set of tasks.
 3. The inventory systemof claim 1, wherein the station is a stow station for loading inventoryitems into the inventory holders; wherein the predicted set of tasksdetermined by the management module comprises stowing tasks of loadinginventory items into the inventory holders; and wherein the managementmodule is configured to instruct the second set of the mobile driveunits to move respective inventory holders having available space forthe stowing tasks from respective initial storage locations torespective subsequent storage locations closer to the stow station. 4.The inventory system of claim 3, wherein the management module isfurther configured to instruct a third set of the mobile drive units tomove respective inventory holders lacking available space for thestowing tasks from respective initial storage locations to respectivesubsequent storage locations further from the stow station.
 5. Theinventory system of claim 1, wherein the station is a count station forcounting inventory items of the inventory holders; wherein the predictedset of tasks determined by the management module comprises countingtasks of counting inventory items of the inventory holders; and whereinthe management module is configured to instruct the second set of themobile drive units to move respective inventory holders having inventorybins with inventory items therein to be counted for the counting tasksfrom respective initial storage locations to respective subsequentstorage locations closer to the count station.
 6. The inventory systemof claim 5, wherein the management module is further configured toinstruct a third set of the mobile drive units to move respectiveinventory holders lacking inventory bins with inventory items therein tobe counted for the counting tasks from respective initial storagelocations to respective subsequent storage locations further from thecount station.
 7. The inventory system of claim 1, wherein the stationis a pick station for unloading inventory items from the inventoryholders; wherein the predicted set of tasks determined by the managementmodule comprises picking tasks of unloading inventory items from theinventory holders; and wherein the management module is configured toinstruct the second set of the mobile drive units to move respectiveinventory holders having inventory items for the picking tasks fromrespective initial storage locations to respective subsequent storagelocations closer to the pick station.
 8. The inventory system of claim7, wherein the management module is further configured to instruct athird set of the mobile drive units to move respective inventory holderslacking inventory items for the picking tasks from respective initialstorage locations to respective subsequent storage locations furtherfrom the pick station.
 9. An inventory system comprising: a plurality ofmobile drive units configured to move a plurality of inventory holdersconfigured to store inventory items, the plurality of mobile drive unitsconfigured to move the plurality of inventory holders among locationsincluding a plurality of stations and a plurality of storage locations,each station of the plurality of stations including at least one stationlocation configured to receive an inventory holder for completion of atask involving at least one inventory item associated with the inventoryholder, each storage location of the plurality of storage locationsconfigured to store an inventory holder when the inventory holder is notat a station location, not being transported en route to the station,and not being transported en route from the station; and a managementmodule configured to: determine possible movements of the plurality ofinventory holders among the plurality of storage locations; determine autility of an arrangement of inventory holders in the plurality ofstorage locations resulting from each of the possible movements; andinstruct at least one of the plurality of mobile drive units to performat least one of the possible movements based on the determined utility.10. The inventory system of claim 9, wherein the management moduleconfigured to determine a utility of an arrangement resulting from eachof the possible movements comprises the management module configured toassign a utility score to each of the possible movements, wherein theutility score of each possible movement is based on at least one of: adrive time involved in the possible movement for a mobile drive unit; anamount of time a mobile drive unit would deviate from other tasks toperform the possible movement; an amount of distance a mobile drive unitwould deviate from other tasks to perform the possible movement; achange in distance of an inventory holder relative to a particularstation provided by the possible movement; a degree to which contents ofan inventory holder moved by the possible movement match criteria ordemands of a particular station; a timeframe of the demands of aparticular station; future gains in total system efficiency provided bythe possible movement; or future losses in total system efficiencyprovided by the possible movement.
 11. The inventory system of claim 10,wherein the management module configured to instruct at least one of theplurality of mobile drive units to perform at least one of the possiblemovements based on the determined utility comprises the managementmodule configured to instruct the at least one of the plurality ofmobile drive units to perform the at least one of the possible movementshaving a utility score exceeding a threshold.
 12. The inventory systemof claim 10, wherein the management module configured to instruct atleast one of the plurality of mobile drive units to perform at least oneof the possible movements based on the determined utility comprises themanagement module configured to instruct the at least one of theplurality of mobile drive units to perform the at least one of thepossible movements having a highest utility score relative to otherpossible movements.
 13. The inventory system of claim 9, wherein themanagement module configured to determine possible movements of theplurality of inventory holders among the plurality of storage locationscomprises the management module configured to determine possiblemovements of the plurality of inventory holders that meet criteriaassociated with tasks that are predicted to be associated with aparticular station.
 14. An inventory system comprising: a plurality ofmobile drive units configured to move a plurality of inventory holdersconfigured to store inventory items, the plurality of mobile drive unitsconfigured to move the plurality of inventory holders among locationsincluding a plurality of stations and a plurality of storage locations,each station of the plurality of stations comprising at least onestation location configured to receive an inventory holder forcompletion of a task involving at least one inventory item associatedwith the inventory holder, each storage location of the plurality ofstorage locations configured to receive an inventory holder for storageof the inventory holder when the inventory holder is not at a stationlocation, not being transported en route to the station, and not beingtransported en route from the station; and a management moduleconfigured to: provide primary instructions to each of a first set ofmobile drive units to at least one of move an inventory holder at astation location, move an inventory holder to a station location, ormove an inventory holder from a station location; and provide secondaryinstructions, to be performed when not performing one of the primaryinstructions, to each of a second set of mobile drive units to move aninventory holder from one storage location to another storage location.15. The inventory system of claim 14, wherein the first set of mobiledrive units includes at least one of the mobile drive units of thesecond set of mobile drive units.
 16. The inventory system of claim 14,wherein the management module is further configured to provide primaryinstructions only to the first set of mobile drive units and providesecondary instructions only to the second set of mobile drive units,wherein the first set of mobile drive units and the second set of mobiledrive units are distinct from one another.
 17. The inventory system ofclaim 14, wherein the management module configured to provide secondaryinstructions to each of a second set of mobile drive units comprises atleast providing secondary instructions to a mobile drive unit to swapstorage locations of at least two inventory holders.
 18. The inventorysystem of claim 14, wherein the management module configured to providesecondary instructions to each of a second set of mobile drive unitscomprises at least providing secondary instructions to at least twomobile drive units to swap storage locations of at least two inventoryholders.
 19. The inventory system of claim 14, wherein the managementmodule is further configured to provide the secondary instructions so asto facilitate moves predicted to be instructed by the primaryinstructions.
 20. The inventory system of claim 19, wherein themanagement module is further configured to provide the secondaryinstructions based on a determined utility of the secondary instructionsfor facilitating the moves predicted to be instructed by the primaryinstructions.